How to Power Automotive Front-End Systems, ADAS Processor – Part 1


Hello and welcome. My name is Ambreesh Tripathi,
and I am an apps engineer at Texas Instruments. The subject of this talk is, How
to Power Automotive Front-End Systems. This talk is split
into three parts. This is the first
part, where I will be covering automotive ADAS
processor power supply design. Here is the agenda
of the presentation. I will go into the details
of automotive front-end power block and also review
two ADAS power solutions. The first one is an example
of a 30 watt automotive ADAS reference design for a
typical surround view system. And this will include
all the protection. And the second
reference design will be a complete
automotive camera module design, where we will go
into the details of EMI requirements, POC
filter requirement, the power over coax
filter requirement, as well as input voltage
transient requirement. This is a generic block diagram
of always on automotive system and all battery conditions. So what are the key features
of the block diagram? Now, the first
feature is the system must maintain a constant
output voltage or the full DC range of battery condition as
specified in the OEM standard. Now, here the Vin can go
down to 3.2 volt simulating a severe cold
cranking condition. Or the input voltage
can go up to 18 volt, simulating the upper range
of normal battery operation. Also, the system
must clamp, filter high voltage electrical
fast transients and maintain operation
through them. These pulses include load dump,
which is specified by OEMs and is about, like,
27 to 30 volts. And it may include other
transients outlined in ISO 7637, part 2 standard. The system must properly also
respond to a reverse polarity event and should shut down. The design should
also comply with CISPR 25 automotive EMI
standard, both radiative, as well as conducted EMI. So here are the details of
automotive front-end design. We have divided the
automotive front-end design into four parts. The first is reverse
battery protection. Also, we will need to have a
transient protection, which we will dig into the details. So we need to have the
reverse battery protection. We need to have a
reboot system here. Also, we will go into the
details of wide Vin buck converter, and the
supervisor if needed. So why do we need
reverse protection for any automotive system? We just need it to
protect the system against the battery
being attached with the reverse polarity. That means you put the
positive and negative in the opposite order. Now, traditionally,
diodes have been used for look and
application, but they dissipate a lot of power
because of the diode drop. In high current application,
traditionally, multiple diodes are used in parallel
to spread the heat. In some cases, high-side
PFET or a low-side NFET with external bias components
is most efficient compared to the diodes, and they
support higher load current. But they are larger
and more expensive. So what is a solution? The solution is to use
a charge pump controller with the high-side NFET,
internal effect, which would provide more
integrated solution and will also reduce
cost and current. Now, let’s go into the details
of pre-boost requirement. First of all, we need to
support the lower Vin. In the case of cold
crank/start-stop, and as well as warm
crank condition. The switcher needs to
switch outside the AM band, either below or
above the AM band. And also asynchronous
solution is more common, particularly for low voltage
and mid-voltage pre-boost application, because of its low
cost and easy designability. So let’s move on to the
requirements of a wide Vin buck converter. Now, the wide Vin
buck converter needs to support voltage up to 36
volt. Also, traditionally, the automotive wide
Vin buck converter used to switch
below the AM band. And what is the
disadvantage of the switcher switching below the AM band? Basically, the harmonics
will still end up in AM band, and it will need
a lot of filtering to filter out the harmonics. Now, when you switch
above the AM band, there will be
absolutely no harmonics. And also, the size of the input
filter will be much smaller, as well as the output inductor,
as well as the capacitor size will be much smaller and will
result in the size minimization of the system. Further, for
synchronous converter, it’s preferred for output
current to be less than or equal to 3 amps. Now, for the supervisors,
they are, basically, used to monitor system
voltages and also to trigger a controlled
power-down sequence when detecting a falling or
out-of-range supply voltages. For point of load DC/DC
converter, remember, what is the input voltage for
point of load DC/DC converter? These are low input voltage– 3.3 volt or 5 volt. And generally, the switcher
switches above the AM band at higher frequency. A multiphase solution
is preferred, interleaving is preferred,
and size is usually a concern in these systems. Therefore, typically, they are a
very small integrated solution, of course, with
high-switching frequency and with very small inductor
and capacitor sizes. To support our automotive
customer, designing ADAS power supply, we have built
a large, library of power solutions optimized
for cost, EMI, and input voltage transients. Input voltage transients,
they show proof of concept and are a great vehicle
for the customer to look at during
the evaluation phase. We will go into the details of
PMP10653, as well as PMP10652. Now, PMP10652 is a ADAS 30
watt system level power supply design with all
automotive protection, as well it meets
the MI standard. PMP 10653 is a complete
camera model design. And we’ll go into the
details of EMI, POC, as well as the transient
requirements there. So this is a system
block diagram of automotive power solution
for a typical surround view ADAS system. So the power solution
ranges from 15 watt to 30 watt for a typical
surround view system. Now, the application
here uses two coil. One is the master, and
another is the slave coil. And each coil in this particular
application needed 4 amp at 1.2 volt output. Now, let’s start with
the front end here. Now, the front-end
protection is taken care of by the [? devious ?]
and the smart diode. So why do we need
[? devious ?] at the front end? So the [? devious, ?] which
act as the transient voltage suppressor, are used to meet
ISO 7637, part 2 plus standard. And the reverse protection is
ensured through smart diode here. Also, the design is tested
against CISPR 25, class 4 regulation limit, and
hence, you can see the EMI filter here used at the input. Now, there are,
like, two LM53603 2.1 megahertz wide
input voltage DC/DC converters used to provide
power to the two coils. We are going to detail of
this exciting 2.1 megahertz automotive switcher
later in the slides. For point of load
solution, we have used DPS57114, which is a point
of load 4 amp, 2 megahertz solution. Here, we have used
charge from DPS60150 to supply the power
for CAN communication. This architecture eliminates
the need of pre-boost at the input for
start stop application and thereby reduces the cost. You can see with the
front-end DC/DC converter, even with this
high-searching frequency, we can have a 2.3 volt output at
the wide input voltage from 4.5 volts up to 36 volt input. And hence, even if
you have input voltage of 6 volts at the input, in the
case of start-stop application, or 4.5 volts in the case
of warm-crank condition, this DC/DC converter will still
maintain a 2.3 volt output here. And hence, you don’t need
a pre-boost at the input. And for 5 volt
CAN communication, you can just use a
charge pump here. PMP10652 is a 30 volt
ADAS system power-driven design with EMI compliances. The design uses all the parts
which are automotive qualified. For that, all the
DC-DC converters used in this system use
switches above the AM band. Also, we have used 4-layer board
for this particular design. Now, let’s go into the details
of this exciting true 2 megahertz DC/DC converter, which
provides front-end solution for the ADAS design. Now, this particular
DC/DC converter is, of course, a fully
integrated DC/DC converter. It’s synchronous. It offers a 2 amp
or 3 amp output. And this is a true 2
megahertz DC/DC converter. So now, first, let’s go into
the detail of true 2 megahertz DC/DC converter, and we will
come back to this slide again. So what is true 2
megahertz DC/DC converter? Putting 2 megahertz
on the data sheet is very easy as most DC/DC
will operate at that frequency. But in reality, how the
device operates at that speed is more important, as
it affects the system. Here, as you can see in this
graph of searching frequency versus input voltage,
the red trace represents the
performance of LM53603. And the blue trace here
represents the performance of the competitor device. Now, what do you see at
the high input voltage when the minimum
ON time is reached? The blue trace here
exhibits poor performance when the minimum ON time is
reached at the higher input voltage. Now, again, the blue trace will
exhibit poor noise performance and will likely need
additional circuit to compensate for the behavior. Now, you compare that with
the LM53603 performance at the high input voltage. But there is a smooth
frequency foldback. When the minimum
ON time is reached, you can see as most
frequency foldback, and hence, offers a
much better solution at higher input voltage. Now, let’s move on
to our deep drop out condition at the
lower input voltage. Now, here again,
you can see LM53603 has much better performance
compared to the competitor device. And what is the reason? The reason is the much smaller
minimum OFF time compared to the other switcher here. So [INAUDIBLE] LM53603 perform
at 2 megahertz or wide input voltage. You can see here from
close to 7 volt up to 20 volt input at full load. You can expect this
DC/DC converter to switch above the AM band. Now, let’s return
back to this slide again and look at the
transient performance when there’s a load
transient here. Now, towards your right,
you can see two graphs. One, which is, basically,
the performance of LM53603 and the other, which is
performance of a competitor device at the high Vin voltage. Now, the data is taken
at 28 volt input. Now, what you can see is
at high input voltage when the minimum ON time is
reached, the competitor device performed very poorly,
and just a moment ago we were talking about it. You can see very high ripple. And even more problematic
is the transition from high load to no load– and you can see this
or should– which can kill other systems connected
to the output of this DC/DC converter. Now, compare this
performance with LM53603 load transient performance. You can see absolutely
no noise here at the no load, as well as
the transient here is minimum. And it’s because we
have already taken care of these
automotive requirements. And hence, LM53603
performs much better compared to most of these
DC-DC converters of level in the market. Also, this particular
device supports up to 150 degrees C
junction temperature and also have excellent light
load efficiency and the IQ in the range of 20 microamps. So we tested the MP10652 volt
for conducted EMI performance. And as you know, for a conducted
EMI for automotive system, we need to do two tests. One test is from
0 to 30 megahertz, and another is from
30 to 108 megahertz. And the critical
is the performance in the FM band, which
is from 88 megaheretz to 108 megahertz, which is
more stringent to comply with. Now, this particular
solution complies with CISPR 25, class 4. And, you know, for
EMI optimization for any automotive design,
it is very important to choose IC with pinouts
that were designed with EMI performance in mind. So in all our new
automotive DC/DC converters, we have tried to innovate with
both packaging and pinouts to optimize EMI performance. What you can see here is Vim
is based next to the PGND. So what is the advantage
of doing this pinout here. Basically, you can place
the high frequency bypass capacitor, which will
minimize the critical input loop, and thereby,
will reduce the EMI. So remember, you have a
discontinuous input current in the buck
converter, which will result into the
input voltage ripple and will generate the EMI. Also, the CBOOT is based
next to the switch node. And by doing so, again, we
minimize the loop area here, so that you can put small
[INAUDIBLE] in switch node, as well as between the CBOOT. The feedback
components now can be referenced to the [INAUDIBLE]. And remember, this feedback
is also away from this switch node and so that no
noise couples back to this feedback bin and thereby
ensure a stable operation. So by giving this pinout, you
will ensure a good system level layout, and thereby,
will minimize the EMI, enhance the EMI
performance here. This EMI performance is
taken without any common mode choke or shielding. So we’ve already
talked about the EMI. Now, the next big requirement
in any automotive system is the front-end protection
through [? devious. ?] Now, this reference design
was tested against ISO 7637 that specifies positive
and negative pulses. Now the positive
and negative voltage are the results off
inductive wire harness. You know, you have
long wires running in in the automotive system, so
you have the inductive wire harness. Or you may also have parallel
inductive load connected to the automotive system. And the worst part
is these pulses can go up to plus minus 75 volt. Now, the question is, how to
protect the automotive system against these pulses. And the solution is to use the
bidirectional [? devious ?] to clamp both the positive
and negative voltage. But in order to choose this
[? devious ?] here, what do you need to know? First, we need to know
the clamp voltage, and the second, we need
to know the peak power rating of the [? devious. ?]
So let’s go into the parameters here. So the parameter mentioned on
the right bottom of the screen is of ISO 7637 parts 2A,
which simulate transient due to sudden interruption of
currents in a device connected in parallel with device and
that test due to inductance of wiring harness. So what will happen? This will generate, of course,
a positive going pulse here. You can see this positive
going pulse here. Now, for clamping the
positive going pulses. What you need to do–
you need to clamp above the double battery voltage
or the jump start voltage. And also, we need to clamp
above the central load dump voltage, which is specified by
the OEMs, which is typically about 27 volt. But
this clamping voltage needs to be lower than the
maximum operating voltage of the downstream devices. So in this application, 30
volt [? devious ?] is chosen. Now, the 30 volt is
above 27 volt load dump voltage and also the low 36
volt DC/DC converter voltage. Further, we need to know
now the power rating of the [? devious ?] here. You can easily simulate
this transient here. Now the VT1 here can be a 50
volt source with the source impedance of two ohms. Now, first of all,
we need to calculate the current which is flowing
in in the [? devious ?] here. So you have this 30-volt clamp. So 50 volt minus 30 volt divided
by this impedance of 2 ohms. That gives you 10
amp of current. Now when you multiply that 10
amp 30 volt clamp voltage here, you get around 300
volt of dissipation. But you know, the second
[INAUDIBLE] is in what time we need to dissipate that
amount of power, for what time. You can see here that
td, the time duration, is 50 microsecond. So for 50 microsecond, we need
to dissipate 300 volt of power. In this application
we used SMBJ 28A, which can dissipate 600
volt for one millisecond. So this can easily dissipate
this amount of power in our application. Earlier with PMP10652
design, we talked about powering ADAS
processor and peripheral. Now, let’s move on to the remote
camera module design, which communicates with ADAS
processor through Power Line Communication. This is a typical block diagram
of an automotive camera module system. The optical data
first, of course, is converted into distal
data, using a CMOS sensor, [INAUDIBLE] sensor. Here in this particular design
OmniVision distal image sensor OVD 10640 was used. Now, this CMOS sensor will
generate 12 bit parallel data. Now, we need to serialize
this 12 bit parallel data. TI’s best-in-class DS90UB9138
serializer [INAUDIBLE].. But serializers, they borrow
data from the MOS sensor and dump it on the power line. Also, there is an isolation
because between the power and the signal line,
using this high frequency filter, which is referred
to as power or coax filter. Now, the DC/DC
converter was used to provide power solution
to the whole camera module, and we will go into the detail
of this new automotive DC/DC converter. PMP10653 is an automotive
camera module reference design for uncompressed
distal video system. This particular
design is designed for stop start condition. And we have done a lot of
layout optimization for power, as well as signal chain,
which include the coax filter, serializer, and image sensor. The front-end DC/DC converter
used in this particular design switches above the AM
band, 2.1 megahertz. And the most important point
of this particular design is to present a solution in
as small a size as possible. So this particular design was
designed in one inch cross, one inch [? bode ?] space. And all the parts that have been
used and this particular design is all automotive qualified too. Now, we talked about the
automotive front-end DC/DC converter LM536034
ADAS processor. But we have also designed
a different converter for a lower power application
like this, LM53600, as well as LM53601. So LM53600 is capable of
delivering 650 milliamp, and 601 is capable of
delivering 1 amp of current. So this particular
solution, of course, has a 2 megahertz performance
that’s very small in size, but we have included SPEC
spectrum option here. So what is a SPEC
spectrum option? So in most systems
containing these switches, low frequency
conducted emissions from first few harmonic
or for searching frequency can easily be filtered. Our most difficult
criteria is the reduction of the higher harmonics,
which fall into the FM band. These harmonics often
coupled to the environment through electric field
around the switch node. Now, LM53600 and 01 devices
use a plus/minus 4% SPEC of frequency, which spreads the
energy smoothly across the FM band, but it is small enough
to limit the subharmonic oscillation below its
searching frequency. So the peak emission
in the FM band can effectively be
reduced by more than 60 b. You can see the results of
conducted EMI performance of PMP 10653 with the
[? SPEC ?] spectrum and without the
[? SPEC ?] spectrum. So in the design with
the [? SPEC ?] spectrum, you can see the
smoothening of the peak, but clearly at the
higher frequency, and hence, thereby, comply with
CISPR 25, class 5 regulation. And remember, again, there is
no common mode choke, as well as there is no shielding done here. Now, here, without the
[? SPEC ?] spectrum, you can see all those
peaks of the harmonics and it may not comply with the
stringent CISPR 25, class 5 requirements. So apart from EMI, power
or coax filter optimization is most critical for any
automotive camera module design. In Power Line Communication
we have common power and signal conduction line. It’s not like you have a
separate power and a signal line. But if you view from the
signal line, what you do is you introduce a high
frequency filter here, which is nothing
but an inductor. And if you view from the
signal line, impedance of this inductor
and the POC filter, the power over coax filter,
which is this inductor here, increases at higher frequency
and won’t allow any distortion of the data signal line. If you view from the
power line here– so if you use a DC-blocking
capacitor, and hence, the DC line capacitor
blocked the DC power influx into the driver, which
is a serializer here, but the inductor of the POC
filter allowed the DC current to pass through it– you can assume the
transmitter and the receiver here as being camera
model and ADAS processor. Now, how to design
this inductor, which can isolate the
signal and the power line? So an ideal 100
microhenry inductor could work as a low pass
filter with impedance greater than 1 kilo
ohm at frequency. Starting at 1
megahertz, however, due to parasitic capacitance,
a real 100 microhenry inductor will cease to have high
impedance around 70 megahertz. So you can see here the
100 microhenry inductor will have a self-resonance
around here, and you’ll see a decrease
in the impedance. Now, what’s a solution here? The solution here is
to add another inductor in series, which is actually
a 4.7 microhenry inductor. Now, what it will
do, it will ensure we have high impedance or
wide frequency of interest. But if you use these
two inductors in series, the size will
become unmanageable. So what is the solution? So the solution is we worked
with our inductor vendor, and they came up with this
particular inductor, which is ADL3225V-470MD, which is a
47 microhenry inductor, which has a self resonance
beyond 700 kilohertz. Here, as you can
see, 700 kilohertz, which has been represented
by the blue trace. So ADL3225V is represented
by the blue trace here. And you can see here
the self resonance occur at very high
frequency, 700 megahertz, and hence, it offers very high
impedance or a wide frequency range. And you don’t need
to add any further. And this is, again, a
very small inductor, and thereby, you can
achieve size optimization. So for more information, you
can log on to ti.com/tidesigns, and you can go on and
search with the PMP number. With that, we have come to
end of this presentation. Thanks for watching.